There isn't one centralized database with that information for everyone. Each state, and even inside one state each county, maintains their own records, so someone who is born in Florida, gets married in California, and then has a kid born in Oregon would need to contact each of those states for proof of those events if they lost the original copies for whatever reason. There is a national system that can (mostly) check against those state and local level records, but it also has limitations. Passports and birth certificates can be proof of citizenship, but don't prove where you live at the time of the election even if you do have one on hand.
The voter registration process already gives the state enough information to determine whether an individual is eligible to vote in that state. For federal elections (which are still run by the states, just for federal level positions), that includes confirming that the person is a citizen, but each state is able to decide whether to allow noncitizen residents to vote on local government issues or not.
High school sports (plenty of towns put up flags or banners on their streetlights commemorating senior athletes), "generic" seasonal banners (this is definitely just "winter" and not Christmas, wink wink), some towns might put up flags for fairs or similar events on their streetlights. Generally things that might or might not technically count as flags, and aren't really not political but count as non-political to the people in charge of enforcing this proposal.